The NXF family of proteins have emerged as playing important roles in post-transcriptional gene regulation. Most work has focused on NXF1 and we have recently demonstrated that the NXF1 protein regulates the expression of its own gene by binding to a Constitutive Transport Element (CTE). The CTE is present in an alternatively spliced intron and retention of this intron gives rise to a small NXF1 protein. This small protein appears to modulate NXF1 function. The current model held by many is that NXF1 functions as the major export receptor for mRNA in organisms from Drosophila to Humans. In this model, NXF1 acts together with an essential co-factor, NXT1. Direct RNA binding by NXF1 has been proposed to be the exception, rather than the rule. Thus NXF1 is supposed to interact only indirectly on most mRNAs, binding through RNA-binding protein adaptors, such as Aly/Ref and SR-proteins. However, data from several recent studies, including our own, cast some doubts on this model. The fact that NXF1 interacts directly with a CTE RNA element within the NXF1 gene itself demonstrates that NXF1 can interact directly with cellular mRNA. Other data suggests that the major function of adaptor proteins may be to serve in a hand over of NXF1 to the RNA, eventually resulting in a lock-in on the RNA. We also have preliminary evidence to indicate that NXF proteins also function in the export of certain non-coding RNAs (for example 5S rRNA and BC200 neuronal RNA). The overall goal of this application is to learn more about the interplay between the NXF proteins and their cofactors, and to elucidate how this is used to regulate expression of RNA. The proposal has 4 specific aims: Specific Aim 1: To investigate the regulation of expression and function of small NXF proteins. Specific Aim 2: To determine if CTE function and the small NXF1 protein, are essential for general development and/or brain development. Specific Aim 3: To analyze the function of NXF proteins in trafficking of non-coding small RNA. Specific Aim 4: To analyze the function of the MusD and Alu CTEs and the role of NXF proteins in retrotransposition. PUBLIC HEALTH RELEVANCE: This research will focus on the NXF family of proteins that control the process of RNA export in human cells. These proteins play a major role in the development and functioning of many cells and organs in the human body. Thus, the research has relevance for the diagnosis and treatment of several genetic syndromes, cancer and other human diseases.